Can you get older books and classics on Kindle, or are you limited to more recent ones? For instance, I occasionally re-read books, like by Agatha Christie, for example.
You can get almost any book on Kindle. I have a couple on mine that were written before 1900, and all of the old classics like Jane Eyre, and those books are also available, and sometimes in whole sets.
I think that I got the whole collection of Zane Grey books on Kindle for $1.99.
Also, you can do a search at the Kindle store for any topic, and see all of the available books.
So, for example, if you typed in “vegetarian”, you would first see the books with that in the title, and then similar ones, like vegan, or WFPB diet. It also shows which ones you can read with Kindle Unlimited, so I can check those out for free. You can follow authors that you are interested in, so you can read more of their books.
I also use the Overdrive library app, and get online books from there. However, their selection is much smaller than the Kindle Store, plus you have time lengths to return the book, and with Kindle Unlimited, you can keep books as long as you want them, provided you stay under 10 books.
Another thing that should be mentioned here, is called Prime Reading. If you have an Amazon Prime account, then it also includes the Prime Reading library, which is kind of a smaller version of Kindle Unlimited, but does not cost extra.
There is also Amazon First Reads, which gives you (free) a choice from several new books each month, and you can pick whichever one you want from the selection, and it is yours for free.